Power MOSFETs (metal oxide semiconductor field effect transistors) have high switching speeds and require very little gate drive power because of the insulated gate. One drawback of power MOSFETs is on-resistance (Rdson) and its strong positive temperature coefficient. To achieve a high efficiency power MOSFET, Rdson*A must be reduced where the parameter ‘A’ represents device area. The main components of Rdson include the channel, accumulation layer, drift region, and parasitics (e.g. metallization, bond wires, package, etc.). Reduced Rdson*A is particularly important at low switching frequencies, where static losses dominate over dynamic losses.
In some applications such as automotive applications, power MOSFETs can switch too fast which causes problems. To mitigate these problems, Qgsth must be increased where Qgsth is the gate-source charge measured from 0V to the threshold voltage. In conventional solutions, increasing Qgd also increases the ratio Qgd/Qgsth where Qgsth is the gate charge in weak inversion. Increasing the ratio Qgd/Qgsth can cause capacitive turn-on and highly increased losses. Furthermore, due to overly high Qrr (reverse recovery charge) stored e.g. in the border of the die (chip), power MOSFETs are not sufficiently commutation-robust in some applications. Also, conventional power MOSFETs cause high losses because of high forward voltage in forward conduction mode. Accordingly, there is a need to reduce the channel resistance (Rchannel) in order to increase Qgd without significantly changing the ratio Qgd/Qgsth or increasing the risk of capacitive turn-on.